Efforts to improve surgical outcomes and cost structure, particularly with spinal surgery, have led to increased use of minimally invasive procedures. These procedures often use image-guided modalities such as fluoroscopy, CT, nerve stimulators, and, more recently, the Doppler ultrasound test. While often involving less risk than surgery, minimally invasive spinal procedures, pain management procedures, nerve blocks, ultrasound guided interventions, biopsy, and percutaneous placement or open intra-operative placement continue to carry risks of ineffective outcome and iatrogenic injuries, such as infection, stroke, paralysis and death due to penetration of various structures including, but not limited to, organs, soft tissues, vascular structures, and neural tissue such as, catastrophically, the spinal cord. Injuries can occur regardless of practitioner experience because a surgical instrument must proceed through several layers of bodily tissues and fluids to reach the desired space in the spinal canal.
To illustrate, the intrathecal (or subarachnoid) space of the spinal region, where many medications are administered, houses nerve roots and cerebrospinal fluid (CSF) and lays between two of the three membranes that envelope the central nervous system. The outermost membrane of the central nervous system is the dura mater, the second is the arachnoid mater, and the third, and innermost membrane, is the pia mater. The intrathecal space is in between the arachnoid mater and the pia mater. To get to this area, a surgical instrument must first get through skin layers, fat layers, the interspinal ligament, the ligamentum flavum, the epidural space, the dura mater, the subdural space, and the intrathecal space. Additionally, in the case of a needle used to administer medication, the entire needle opening must be within the subarachnoid space.
Because of the complexities involved in inserting a surgical instrument into the intrathecal space, penetration of the spinal cord and neural tissue is a known complication of minimally invasive spine procedures and spine surgery. Additionally, some procedures require the use of larger surgical instruments. For example, spinal cord stimulation, a form of minimally invasive spinal procedure wherein small wire leads are inserted in the spinal epidural space, requires that a 14-gauge needle be introduced into the epidural space in order to thread the stimulator lead. Needles of this gauge are technically more difficult to control, posing a higher risk of morbidity. Complications can include dural tear, spinal fluid leak, epidural vein rupture with subsequent hematoma, and direct penetration of the spinal cord or nerves with resultant paralysis. These and other high-risk situations, such as spinal interventions and radiofrequency ablation, occur when a practitioner is unable to detect placement of the needle or surgical apparatus tip in critical anatomic structures.
At present, detection of such structures is operator dependent, wherein operators utilize tactile feel, contrast agents, anatomical landmark palpation and visualization under image-guided modalities. The safety of patients is reliant upon the training and experience of the practitioner in tactile feel and interpretation of the imagery. Even though additional training and experience may help a practitioner, iatrogenic injury can occur independently of practitioner experience and skill because of anatomic variability, which can arise naturally or from repeat procedures in the form of scar tissue. Fellowship training in some procedures, such as radiofrequency ablation, is not sufficiently rigorous to ensure competence; even with training, outcomes from the procedure are considerably variable. In the case of epidural injections and spinal surgery, variability in the thickness of the ligamentum flavum, width of the epidural space, dural ectasia, epidural lipomatosis, dural septum, and scar tissue all add challenges to traditional verification methods even for highly experienced operators. Additionally, repeat radiofrequency procedures done when nerves regenerate, often a year or more later, are often less effective and more difficult because the nerves' distribution after regeneration creates additional anatomic variability.
No device exists that provides objective, reliable, consistent, real-time feedback of critical tissues and bodily fluids. Further, even the concept of objective device feedback has not been accepted by proceduralists, even though millions of spinal procedures are performed annually as standard of care throughout the world.